Revert "Demonstrate the issue."

This reverts commit 93efa3415ec9cad3aa443efe08c70c61707f40b3.
home.c, dda.c: consider endstops on both axis ends when homing.

Previously, when backing off of X_MIN, X_MAX was also checked,
which of course was already open, so it signals endstop release
even while X_MIN is still closed. The issue exposed only when
endstops on both ends of an axis were defined, a more rare situation.

Essentially the fix simply makes a distinct endstop check case
for each side of each axis.

This even makes binary size 40 bytes smaller for the standard case.
dda.c/.h: reduce debounce counting variable.

As we can always only move towards one end of an axis, one common
variable to count debouncing is sufficient.

Binary size 12 bytes smaller (and faster).